The Milky Way galaxy is composed of millions of stars in a relatively flat structure containing a thin disk and a thick disk. Based on computer simulations and analysis of data on the brightness, position, and chemical composition of about 250,000 stars in the thick disk (collected from two telescopes, one in China and one orbiting in space), astrophysicists Maosheng Xiang and Hans-Walter Rix claim that the thick disk of the Milky Way formed in two distinct phases rather than a single one.
Which finding, if true, would most directly support the researchers’ claim?
Explanation
Context: Astrophysicists Xiang and Rix analyzed ~250,000 stars in the Milky Way's thick disk and claim it formed in two distinct phases rather than one. The question asks what finding would directly support this two-phase formation claim.
Answer: B) There's an age difference of about 2 billion years between certain stars in the thick disk.
Why? A 2-billion-year gap in stellar ages within the thick disk would suggest two separate formation events rather than one continuous process — directly supporting the two-phase claim. A single formation phase would produce a more continuous age distribution.
Traps:
- A) "the telescopes used by the researchers have detected stars of similar ages in both the thick and thin disks" → about similarities between disk types, not about internal age variation within the thick disk
- C) "the thin disk contains about twice as many stars that can be seen from Earth" → about the thin disk's visibility, irrelevant to thick disk formation phases
- D) "the stars in the Milky Way tend to have very similar chemical compositions" → suggests uniformity, which would argue against distinct formation phases